Thermoplastic polymers, such as polyvinyl chloride (PVC) for example, are often utilized in one or both of two general forms: substantially unplasticized and plasticized. The substantially unplasticized forms of thermoplastic polymers may be utilized in applications in which high resistance to chemical substances is required. The plasticized forms of thermoplastic polymers are commonly used in applications where flexibility and pliability are among the most important physical characteristics. These physical characteristics are achieved by compounding a thermoplastic polymer such as PVC with one or more materials which serve as plasticizers following their addition to the thermoplastic resin. Broadly defined, plasticizers are high boiling point liquids. These liquids do not evaporate from the matrices they are added to, but rather remain in the polymer matrix to preserve flexibility, pliability, and adhesiveness. Plasticizers currently in industrial use generally are petroleum-derived phthalates and benzoate compounds. Dioctyl phthalate (DOP) and diallyl phthalate (DAP) are examples of petroleum-derived compounds commonly used as plasticizers for PVC.
Petroleum-derived plasticizers may be subject to several significant limitations. In addition to being processed from a nonrenewable source, such plasticizers may be expensive to produce due to fluctuations in the price and availability of crude oil. Furthermore, petroleum-derived plasticizers such as DOP are suspected to disrupt human endocrine activity. Therefore, it may be desirable to limit the use of petroleum-derived plasticizers in certain situations, especially when the plasticized product comes into human contact at ambient temperature and especially at elevated temperature. Thus, there is a need for a low-cost, non-toxic, environmentally safe alternative to the petroleum-derived plasticizers that are currently incorporated into consumer products. Plasticizers which are derived from vegetable oils provide such an alternative.
However, unmodified vegetable oils are largely incompatible with thermoplastic polymers such as polyvinyl chloride resin. Certain types of modified derivatives of vegetable oils, such as epoxidized soybean oil, have been investigated as possible plasticizers, as exemplified in the disclosures of U.S. Pat. Nos. 6,734,241; 6,797,753; and 6,949,597 and U.S. Pat. Publication No. 2010/0010126. Although such derivatives may provide certain advantages over unmodified vegetable oils, there is continued need for even further improvement in the performance and characteristics of plasticizers obtained from renewable resources such as plants.